Creating Spinal Implants Using Additive Manufacturing

Renishaw, a global engineering company, worked with two pioneering technology organizations to verify the ability of metal additive manufacturing (AM) technology to create lightweight spinal implants that reflect the mechanical characteristics of bone.

As part of the project, Irish Manufacturing Research (IMR), a manufacturing research organization, designed and engineered a range of representative spinal implants. IMR used software from nTopology to design the implants and manufactured them using a Renishaw RenAM 500M metal AM system.

Background

Based in Dublin, IMR supplies Irish manufacturing companies with the support required to be confident in the next generation of digital manufacturing.

Medical device production is a widespread industry in Ireland and IMR collaborates with a wide range of organizations to evaluate what can be attained with the use of 3D-printed medical devices.

An industry-leading generative design company located in New York, nTopology has produced next-generation design engineering software for advanced manufacturing.

The exclusive software platform from nTopology allows for the production of intricate, performance-driven designs that fully make use of the capabilities of additive manufacturing.

Image Credit: Renishaw Plc

These cutting-edge designs can be made in minutes rather than hours or days. nTopology's Platform allows manufacturing processes, engineering workflows, and knowledge to be gathered within the software, which helps users to produce tailored workflows to reach their specific requirements.

Spinal implants are required to restore intervertebral height in patients with various medical conditions such as osteoporosis, spinal stenosis, spondylolisthesis, herniated discs, and degenerative disc disease.

Thanks to all the support we have received from Renishaw developing spinal implants as well as working on other projects, we have up-skilled our staff and are now well established in the AM space.

Renishaw worked tirelessly with us on improving the AM process for producing the spinal implants. Together, we designed a set of experiments that yield the most appropriate parameter settings for the product. As a result, we reduced the amount of post-processing required on key features by a factor of ten.
 

Irish Manufacturing Research (IMR) (Republic of Ireland)

Challenge

Traditional manufacturing methods cannot create spinal implants with a lattice structure. This structure provides a high surface area to promote the migration of osteoblasts into the implant and offers the ability to enhance the mechanical features of a porous volume to adhere to the necessary loading conditions.

IMR recognized metal AM as an appropriate technique to produce lattice structures optimized for osseointegration, but the best AM machines and design software were yet to be identified.

“The capabilities of AM hardware have developed fast and are now outpacing traditional design tool capabilities,” described nTopology's Director of Business Development and Partnerships, Duann Scott.

“nTopology was established in 2015 when the founder realized there was no software that could design the complex geometries AM was capable of producing.

Image Credit: Renishaw Plc

Image Credit: Renishaw Plc

To allow a smooth AM workflow from design to manufacture, hardware and design software need to communicate effectively,” Scott added.

“Easy translation from design software to an AM machine is especially important when producing spinal implants, because intermediary stages and information transfer provide opportunities for errors and inconsistencies to occur.”

Solution

Renishaw, nTopology, and IMR worked together to create implants for the cervical spine (c spine) that included lattice structures utilizing AM. The name of the project for the implant type being Anterior, Cervical, Interbody Device, or ACID.

IMR firstly made a design envelope to determine the specific opportunities demonstrated by AM to enhance patient outcomes. nTopology then supplied the software required to plan the intricate geometry of the spinal implants and Renishaw's RenAM 500M machine was utilized to produce the implants by means of AM.

IMR performed thorough research to find the correct dimensions for the specified case and the loading conditions that the implants must undergo in daily life. Extreme situations, for example jumping or running, were also accounted for.

This data was used in combination with the known material characteristics of bone in patients with diseases that are responsible for creating the need for a spinal implant.

The three companies then collaborated in designing the mechanical features of the device. The features are mostly a result of the geometry of the unit cells utilized in the lattice structure to attain mechanical features similar to those of human bone and to enhance the porous lattice for osseointegration.

When the parameters for the design of the implants were chosen, IMR created the design files utilizing the nTop Platform. nTopology and Renishaw closely worked together to ensure the compatibility of their products, so that a design could be easily transferred from the nTop Platform to the RenAM 500M.

IMR then utilized the RenAM 500M to create prototypes from grade 23 titanium (Ti 6Al-4V ELI).

Image Credit: Renishaw Plc

The company carried out a range of investigations to verify that the device was in line with the most relevant elements of the standard specifications enforced by the FDA.

The chemical features were evaluated to ensure that ASTM F136 and ASTM F3302 were met, the standard specification for wrought grade 23 titanium to be employed in orthopedic implants and the standard specification for the additive manufacturing of titanium alloys by powder bed fusion respectively.

The mechanical features of the porous structure were characterized in line with ISO 13314, a test technique employed to establish the failure mode and compressive features of a porous metallic material.

Lastly, further testing verified compliance with ASTM 1104 and ASTM 1147, the standard test techniques to show that porous structures do not delaminate from the device’s solid faces.

“To demonstrate proof of concept, we built witness coupons on the RenAM 500M build plate and performed destructive testing of the coupons,” recalled Sean McConnell, Senior Research Engineer at IMR. “We did this to ascertain the chemical, metallurgical, and mechanical properties of the implants.”

Results

This proof of concept study verified that AM can be utilized to create spinal implants with features that are impossible to attain with traditional manufacturing techniques.

The RenAM 500M was employed for manufacturing the final implants and the prototypes, so the process did not have to be translated for various machines. This streamlined workflow will create extensive time and cost reductions for manufacturers of medical devices.

“Two years ago, AM in IMR was non-existent,” described McConnell. “Thanks to all the support we have received from Renishaw developing spinal implants as well as working on other projects, we have up-skilled our staff and are now well established in the AM space.”

“We have been able to pass the knowledge about AM gained from Renishaw to our customers,” said McConnell. “We are working with companies who were previously fearful of the risks associated with the AM knowledge gap but are now building their confidence using AM equipment.

Image Credit: Renishaw Plc

“Renishaw worked tirelessly with us on improving the AM process for producing the spinal implants,” McConnell added. “Together, we designed a set of experiments that yield the most appropriate parameter settings for the product. As a result, we reduced the amount of post-processing required on key features by a factor of ten.”

“IMR is instrumental in bringing advanced manufacturing technology to the Irish industry,” described Ed Littlewood, Marketing Manager of Renishaw's Medical and Dental Products Division.

“The company's design expertise and research rigor enabled the production of representative spinal implants that demonstrate the potential of AM to transform healthcare.”

Along with showing the ability of AM to create spinal implants, this study demonstrates that by considering design for additive manufacturing (DfAM) at the initial stages, a reduction of reliance on supports is possible which results in a reduction of finishing operations.

“The spinal implants project allowed us to develop our understanding of medical device production and the capabilities of AM machines,” added Scott. “This enabled us to develop our design software so that it can be used to drive the use of advanced manufacturing technology for medical devices.

“There was a considerable amount of trial and error involved in adapting the software to align with the requirements of the RenAM 500M,” explained Scott.

“However, Renishaw's engineers made the entire process smooth and efficient. Projects like this usually take years, but the excellent collaboration between nTopology, Renishaw and IMR meant that we could complete the study in a matter of months.

“We will continue to work closely with Renishaw to ensure companies can access AM technology. We want to encourage wider collaboration in the advanced manufacturing industry,” Scott concluded.

This information has been sourced, reviewed and adapted from materials provided by Renishaw plc - Additive Manufacturing for Healthcare Applications.

For more information on this source, please visit Renishaw plc - Additive Manufacturing for Healthcare Applications.